Genetic regulation of linolenic acid concentration in wild soybean Glycine soja accessions

Soybean [Glycine max (L.) Merr.] oil from current commercial cultivars typically contains ca. 8% linolenic acid. Inheritance studies have shown that linolenic acid concentration in soybean seed is determined by at least two genes which govern activity of the predominant ω-6 and ω-3 desaturases. Selection of germplasm exhibiting homozygous recessive alleles that encode these desaturases has enabled development of soybeans having less than 3.0% linolenic acid. However, accessions of the wild ancestor of modern soybean cultivars, Glycine soja (Sieb. and Zucc.), have oils containing twice the highest linolenic acid concentration found in normal G. max cultivars. Although little is known about inheritance of linolenic acid in wild soybean, it would appear that additional or alternative forms of genes may govern its synthesis. To test this hypothesis, cultivated soybean germplasm was hybridized with wild soybean genotypes having significant differences in linolenic acid concentration. Seed of F₃ progeny from these G. max x G. soja populations exhibited distinct segregation patterns for relative estimates of ω-6 and ω-3 desaturase activity. Frequency class distribution analyses of the segregation patterns, and linear relations between median ω-6 or ω-3 desaturation estimates and corresponding linolenic acid concentration among allelic classes from these populations suggested the high-linolenic acid trait in wild soybean genotypes was determined by a set of desaturase alleles that were different from corresponding alleles in G. max. Introgression of these alternative alleles in G. max germplasm opens a new avenue of research on the genitic regulation of linolenic acid, and may lead to the production of highly polyunsaturated soybean oils for various industrial applications.     

Estimating soybean seed protein and oil concentration before harvest

Temperature and precipitation during the growing season have been shown to influence the protein and oil composition of the soybean [Glycine max L. Merr.] seed. A method based on these parameters was developed to estimate protein and oil concentrations of the seed before harvest. This method was developed with protein and oil data and temperature and precipitation data from the Uniform Soybean Tests, Southern Region, for the years 1975 to 1983. Classification and regression “tree-based” analyses were used to determine the month and numeric value (“splitting point”) of the environmental variable that correctly classified the variation from median protein and oil composition for the 126 location-years. Temperature in September was most influential in determining the splitting point for three of the four variables. Oil concentrations from the location-years were separated into low vs. high median-based boundary categories most readily by the September sum of minimum temperatures. Total protein and oil concentrations from the location-years were classified best by September growing degree days. Protein-to-oil ratios were best separated by the September mean minimum temperature. The August mean maximum temperature best separated protein concentration. These data demonstrate that temperature during specific months of the crop year were useful in estimating the final concentration of protein and oil in the seed and could be used by seed processors to estimate seed composition before harvest.     

Use of NMR for predicting protein concentration in soybean seeds based on oil measurements

Increasing the level of protein in soybean seeds has been a major target for soybean [Glycine max (L.) Merr.] breeders. The objective of this study was to examine the potential of predicting soybean seed protein based on oil values as determined by NMR. Seed protein and oil concentrations were determined in an F₂ population generated from the cross between a G. max (NK, S08-80), and a G. soja (PI 458536) cultivar. The protein concentration in the population ranged from 40.4 to 52.6%. Protein-oil regression analysis was used to generate an equation for predicting seed protein concentration based on oil readings. The regression equation Protein=62.3–1.3 [Oil] (R ²=0.46) was developed, with a corresponding correlation of −0.69 between the traits. With this equation, the mean protein concentration of the selected 25% of the population (a simulated breeding pressure) was greater than the mean of the unselected population (46.1%, SE=0.13) by about 1.9%. Individual F₂ plants that exceeded the mean protein value of the population constituted 86.4% of the selected samples. Selection based on oil concentration, however, failed to include 27.1% of the plants that were among the top 25% for protein concentration. Selection of high-protein plants based on NMR oil measurement was reasonably effective in the test population and might offer a new and rapid method of selecting high-protein individuals in soybean populations derived from the wild soybean progenitor, G. soja. If further tested on other populations and samples, it might be used as an analytical alternative for an indirect measurement of protein concentration based on NMR measurements of the oil.     

Oxidation of acylglycerols and phosphoglycerides by soybean lipoxygenase

Lipoxygenase (EC 1.13.11.12) catalyzes the incorporation of oxygen into polyunsaturated fatty acids, resulting in the formation of their corresponding hydroperoxides. The ability of a commercial preparation of soybean (Glycine max L. Merr.) lipoxygenase to catalyze the oxidation of acylglycerols and phosphoglycerides was investigated. The oxidation rate of trilinolein increased nearly 100% when 5 mM deoxycholate was added to the reaction medium. With further increases in the concentration of deoxycholate, the oxidation rate decreased slightly. The pH profile of trilinolein oxidation was bell-shaped. The rate of oxidation was maximal at pH 8, and it decreased to near zero at pH 5 and pH 11. Even under optimal conditions, the rate of trilinolein oxidation was only 3% of that of linoleic acid, and analysis of time course data showed that, at most, 15% of available linoleate was oxidized. In contrast to the slow rate of trilinolein oxidation, tested phosphoglycerides and diacylglycerols were oxidized at moderate rates. The rate of phosphoglyceride oxidation depended upon the structure of the polar head group and varied between 7–28% of the rate of linoleic acid oxidation. Diacylglycerols reacted at a rate that was 40% of that of linoleic acid. Analysis of the time course of 1,3-dilinolein oxidation showed that as much as 67% of the available linoleate could be converted to the corresponding hydroperoxide. Analyses by high-performance liquid chromatography revealed that more than 20% of the 1,3-dilinolein was converted to unidentified products that are not hydroperoxides.     

Genomic regions governing soybean seed nitrogen accumulation

Nitrogen accumulation in the form of seed protein takes place in soybean [Glycine max (L.) Merr.] during the reproductive stages of development. The purpose of this study was to relate genotypic differences in seed nitrogen accumulation with genomic regions controlling nitrogen accumulation in soybean during R₅, R₆, and R₇ growth stages. A population of 101 F_6∶8 recombinant inbred lines (RIL) developed from a cross of N87-984-16×TN93-99 was utilized. The RIL were grown at the University of Tennessee, Knoxville Experiment Station, in a randomized complete block design with three replications in 2002. Seed nitrogen was determined from pod samples harvested at the R₅, R₆, and R₇ growth stages. A significant (P<0.05) difference among genotypes was found for nitrogen accumulation at all three growth stages. Single-factor ANOVA revealed that quantitative trait loci (QTL) governing nitrogen accumulation in soybean seed were distributed in the linkage groups A2, B2, D1a, D1b, E, G, and M. Phenotypic variation explained by an individual QTL ranged from 5 to 11.6%. These QTL may provide useful marker-assisted selection opportunities for soybean protein improvement.     

A method to estimate soybean seed protein and oil concentration before harvest

Temperature and precipitation variables during linear seed fill are known to be environmental determinants of protein and oil composition of the soybean [Glycine max (L.) Merr.] seed. However, the contribution of other precipitation and temperature events during the growing season and a method that would determine the precipitation and temperature variables most related to protein and oil concentration values of the seed has not been fully explored. The former was evaluated by comparing monthly temperature and precipitation variables of the growing seasons to protein and oil data for the years 1959 to 1996 from three locations listed in the Uniform Soybean Tests, Northern Region. The data set comprised locations from Maturity Groups II and III and consisted of 186 location-years. Classification and regression “tree-based” analysis were conducted to determine the month, environmental variable, and “splitting” points that correctly classified most of the 186 location-years for below-vs.-above-median protein or oil composition. The protein concentrations from the location-years were separated into these two median-boundary categories most readily by temperature variables from the months of April and August. The oil concentrations from the location-years were classified best by August and September temperature variables and precipitation in May and September. The sum of protein and oil concentrations from the location-years were best separated by August and July temperature variables and precipitation in May and July. The protein-to-oil ratios from the location-years were best separated by September precipitation and July and June temperature variables. These data demonstrate that tree-based models can use monthly temperature and precipitation variables during linear seed fill and other specific months of the crop year and relate them to the final protein and oil concentration in the seed. These results could be used by the processing industry to estimate seed composition before harvest.     

Relation between diacylglycerol acyltransferase activity and oil concentration in soybean

Diacylglycerol acyltransferase (EC 2.3.1.20; DGAT) catalyzes synthesis of triacylglycerol from acyl-CoA and diacylglycerol. Activity of this enzyme and developmental changes in oil accumulation were estimated at various stages of seed growth in soybean germplasm with phenotypic differences in oil content. Oil deposition in seed of these genotypes followed a sigmoid pattern that was modeled to predict incremental rates of oil accumulation during seed development. A strong positive correlation was found between the estimated peak rate of oil deposition (near the mid-term of seed development) and oil concentration in mature seed. At saturating substrate levels, DGAT activity measured near the peak rate of oil deposition also was correlated positively with oil phenotype. In the latter stages of seed development, a positive correlation between estimates of enzyme activity at or below the apparent K _m for diolein and comparable oil accumulation rates was attributed to reduced synthesis of substrates and/or potential change in affinity for substrate as suggested by an increase in apparent K _m for diolein in older seed. These data indicated that DGAT activity may be a rate-limiting step in triacylglycerol synthesis. However, it is difficult to accept the idea of a single rate-limiting step at the end of a complex metabolic pathway. Because oil is a quantitatively inherited trait, several genes determine genotypic differences in oil content among soybeans. Hence, DGAT activity may be an indicator of coordinated genetic expression of gene-products in the entire glycerolipid synthetic pathway for a given genotype. In any case, results of this investigation demonstrated that genotypic differences in DGAT activity contributed to expression of genetic variation in oil content among soybean gemplasm.     

Effect of temperature on linolenic acid loss and 18:3 Δ9-cis, Δ12-cis, Δ15-trans formation in soybean oil

Oil was extracted from soybeans, degummed, alkalirefined and bleached. The oil was heated at 160, 180, 200, 220 and 240°C for up to 156 h. Fatty acid methyl esters were prepared by boron trifluoride-catalyzed transesterification. Gas-liquid chromatography with a cyanopropyl CPSil88 column was used to separate and quantitate fatty acid methyl esters. Fatty acids were identified by comparison of retention times with standards and were calculated as area % and mg/g oil based on 17:0 internal standard. The rates of 18:3ω3 loss and 18:3 Δ9-cis, Δ12-cis, Δ15-trans (18:3c,c,t) formation were determined, and the activation energies were calculated from Arrhenius plots. Freshly prepared soy oil had 10.1% 18:3ω3 and no detectable 18:3c,c,t. Loss of 18:3ω3 followed apparent first-order kinetics. The first-order rate constants ranged from .0018±.00014 min⁻¹ at 160°C to .083±.0033 min⁻¹ at 240°C. The formation of 18:3c,c,t did not follow simple kinetics, and initial rates were estimated. The initial rates (mg per g oil per h) of 18:3c,c,t formation ranged from 0.0031±0.0006 at 160°C to 2.4±.24 at 240°C. The Arrhenius activation energy for 18:3ω3 loss was 82.1±7.2 kJ mol⁻¹. The apparent Arrhenius activation energy for 18:3c,c,t formation was 146.0±13.0 kJ mol⁻¹. The results indicate that small differences in heating temperature can have a profound affect on 18:3c,c,t formation. Selection of appropriate deodorization conditions could limit the amount of 18:3c,c,t produced.     

Sucrose fatty acid esters enhance efficiency of foliar-applied urea-nitrogen to soybeans

A greenhouse study is described showing the effect of sucrose fatty acid esters (SFE) applied to soybeans (Glycine max (L.) Merrill cv Fukuyutaka) during the flowering and/or pod-filling periods on the efficiency of foliar-applied urea-nitrogen. SFE applied in combination with urea delayed senescence and when applied during both the flowering and pod-filling periods increased seed yields by 103% and nitrogen accumulation by 132% as compared to urea alone. Average total recovery of¹⁵N-urea in the above ground portions of the plant was 20.6%. SFE combined with urea increased the average recovery to 34.8%. Recovered¹⁵N-urea was only a small portion of the total nitrogen content of the plant. The yield increase resulting from a foliar application of urea may have been due to the leaves continuing to export photosynthates to the nodules hence maintaining the nodules' nitrogen fixing activity for a longer period of time. The addition of SFE to the urea solution increased the retention and/or absorption of urea and increased translocation of urea-nitrogen to the seeds.     

Fatty acid variation in seed oil amongOcimum species

Content, fatty acid composition, and glyceride profile of oil from seeds of seven basil (Ocimum sp.) chemotypes were determined. The species studied includedO. basilicum, O. canum, O. gratissimum, andO. sanctum. The oil content ranged from 18 to 26%, with triglycerides comprising between 94 and 98% of extracted neutral lipids. The major acylated fatty acids were linolenic (43.8–64.8%), linoleic (17.8–31.3%), oleic (8.5–13.3%), and palmitic acid (6.1–11.0%). Linolenic acid was similar among the fourO. basilicum chemotypes (57–62%), highest inO. canum (65%), and lowest inO. sanctum (44%). Basil seed oil appears suitable as an edible oil or can be used for industrial purposes, and could be processed in the same way as linseed oil. Preliminary calculations estimate that a hectare of basil could produce from 300 to 400 kg of seed oil.     

Variation in fatty acid content and seed weight in some lauric acid richCuphea species

Significant genetic variation for lauric acid (12∶0) and capric acid (10∶0) composition and seed weight was measured within lauric acid-rich, self-pollinating germplasm accessions ofCuphea wrightii, C. tolucana, andC. lutea. Means and ranges of individual plant progenies for 12∶0 content ofC. wrightii accessions was 60.5±.63% (49.8±65.8%), 10∶0 content was 23.7±.54% (18.6±33.0%), and 1000-seed weight was 1.50±.03 g (1.20–2.47 g). Progenies of single plant selections carried to the S₂ generation exhibited reduced variability within selections, but significant variation among selections for 12∶0, 10∶0 and 1000-seed weight. Variation among single plant selections ofC. tolucana was less than that ofC. wrightii and attributed to a restricted germplasm base. Means and ranges for 12∶0 content were 61.6±.47% (59.2–69.9%), 10∶0 was 22.3±.62% (11.7–25.3%), and 1000-seed weight was 1.40±.05 g (0.90–1.69 g).Cuphea lutea has a significantly different 12∶0−10∶0 profile than the other lauric acid-rich species. Means and ranges for 12∶0 were 36.8±.14% (33.7–40.8%), 10∶0 was 21.8±.08% (16.4–23.9%), 1000-seed weight was 2.26±.02 g (1.82–272 g). The 1000-seed weight was highly positively correlated with 8∶0, 10∶0, 18∶1 and 18∶2 contents and highly negatively correlated with 12∶0, 14∶0 and 16∶0 in bothC. wrightii andC. tolucana. No such relationship was found forC. lutea. A highly significant negative correlation was also measured for 12∶0 and 10∶0 contents inC. wrightii andC. tolucana.     

Temperature and cultivar effects on soybean seed oil and protein concentrations

The soybean [Glycine max (L.) Merr.] industry is interested in cultivar and climate effects on seed composition. These factors may underlie the known geographic variation in seed protein and oil concentrations. Regression analyses were used to test hypotheses of the effect of temperature and cultivar on oil and protein concentrations of soybean seed using a large data set from the U.S.A. Soybean Uniform Tests. The data set included 20 cultivars representing 10 maturity groups across 60 locations (latitude 29.4 to 47.5° N) for a total of 1863 cultivar by location by year observations. Temperature was determined for each observation as the average daily mean temperature from predicted first pod (first pod at least 5 mm long), using the SOYGRO phenology model, to observed maturity. The mean temperature ranged from 14.6 to 28.7°C among the observations. Linear, quadratic, and linear plateau regression models of oil and protein concentrations vs. temperature were evaluated. The quadratic model gave the best-adjusted R ² values for oil and protein with temperature, of 0.239 and 0.003, respectively. The analyses showed that the oil concentration increased with increasing temperature and approached a maximum at a mean temperature of 28°C. Unaccounted variation in the protein concentration may be from other factors such as photoperiod, water stress, or high temperatures during seed fill. Protein plus oil had a linear relationship with temperature (adjusted partial R ²=0.183). These data document the contribution of climate and cultivar to geographic variability of oil and protein concentrations in the United States.     

Fatty acid composition of some pine seed oils

The fatty acid composition of seeds from seven species of the genusPinus (P. pinaster, P. griffithii, P. pinea, P. koraiensis, P. sylvestris, P. mughus, andP. nigra) was established. Pine seeds are rich in oil (31–68% by weight) and contain several unusual polymethylene-interrupted unsaturated fatty acids with acis-5 ethylenic bond. These are thecis-5,cis-9 18:2,cis-5,cis-9,cis-12 18:3,cis-5,cis-11 20:2, andcis-5,cis-11,cis-14 20:3 acids, with a trace ofcis-5,cis-9,cis-12,cis-15 18:4 acid. Their percentage relative to total fatty acids varies from a low of 3.1% (P. pinea) to a high of 30.3% (P. sylvestris), depending on the species. The majorcis-5 double bond-containing acid is generally thecis-5,cis-9,cis-12 18:3 acid (pinolenic acid). In all species, linoleic acid represents approximately one-half the total fatty acids, whereas the content of oleic acid varies in the range 14–36% inversely to the sum of fatty acids containing acis-5 ethylenic bond. The easily available seeds fromP. koraiensis appear to be a good source of pinolenic acid: their oil content isca. 65%, and pinolenic represents about 15% of total fatty acids. These values appear to be rather constant.Pinus pinaster, which is grown on several thousand acres in the southwest of France, is an interesting source ofcis-5,cis-11,cis-14 20:3 acid (7% in the oil, which isca. 35% of the dehulled seed weight), an acid sharing in common three double bonds with arachidonic acid. Apparently,P. sylvestris seed oil contains the highest level ofcis-5 double bond-containing acids among pine seed oils that have ever been analyzed.     

Environmental effects on fatty acid levels in soybean seed oil

FA composition determines the quality of vegetable oil. Soybean breeders have generated and used mutations in FA genes to develop altered FA profiles in the seed. However, the expression of the alleles and the relative activity of the gene products are often dependent on the environment, and these facts have hampered the breeding efforts. To investigate the environmental effect on FA composition of soybean seed oil in specific mutant material developed at the University of Guelph, a recombinant inbred line (RIL) population was developed from a cross between a low palmitate (16∶0) line and a high-stearate (18∶0) parent. The RIL population was field-tested across three environments over 2 yr. A combined ANOVA for FA composition was conducted to determine the year and location effects on the expression of FA alleles in this material. The results indicated that linolenic (18∶3) level was most vulnerable to the environmental changes. Year effects accounted for a greater amount of variance than location effects for 16∶0, 18∶0, and 18∶1, whereas location effects were more important than year effects for the relative amounts of 18∶2 and 18∶3. Genotype × environment (year, location) interaction effects were significant for the relative amounts of all five FA according to the combined ANOVA. Our results indicated that the extreme minimum daily temperatures during September seed fill period, rather than the means or the maximum temperature, may be responsible for the ratio of saturated vs. unsaturated FA in soybean oil.     

Molecular mapping and identification of soybean fatty acid modifier quantitative trait loci

Altering FA content in soybean [Glycine max (L.) Merr.] oil for improved functionality is a research goal of many soybean breeders. Several of the genes that alter palmitic, stearic, oleic, linoleic, and linolenic acids are modifier genes with small effects, causing these FA traits to act as quantitative traits. The objective of this study was to identify modifier FA quantitative trait loci (QTL) in soybean. A recombinant inbred line population was created from two prominent ancestors of currently available U.S. cultivars (Essex and Williams) and grown in five environments. One hundred simple sequence repeat markers spaced throughout the genome were mapped in this population. QTL were found for all five FA traits on the soybean linkage groups C2, D2, D1b, F, K, and L. A single marker interval on linkage group L contained the largest QTL for palmitic (r ²=13.1%), oleic (r ²=35.3%), linoleic (r ²=50.5%), and linolenic acids (r ²=24.8%); however, this interval also contained the gene for growth habit (Dt1) and was significantly associated with maturity. Other modifier QTL found in this study may be of use in marker-assisted selection to enable breeders to increase genetic gains for desirable FA composition of soybean.     

A new approach to genetic alteration of soybean protein composition and quality

Although soybeans produce high-quality meal, modern animal and fish production systems often require synthetic essential amino acid supplements to fortify feed rations. However, biotechnology may enable development of soybeans with naturally adequate levels of certain essential amino acids for advanced feed formulations. One approach involves genetic manipulation of glycinin (11S) and β-conglycinin (7S) contents, the principal components of soybean storage proteins. Because 11S contains more cysteine and methionine than 7S protein, a higher 11S:7S ratio could lead to beneficial changes in the nutritional quality of soybean meal. Although genotypic variation for 11S:7S may be low among soybean [Glycine max (L.) Merr.] germplasm, ratios ranging from 1.7–4.9 were observed among accessions of the wild ancestor of cultivated soybean (Glycine soja Sieb, and Zucc.). Thus, wild soybean germplasm was evaluated as a potential source of genes that govern protein synthesis that may have been lost during the domestication of G. max. Change in the amount of 11S protein accounts for a significant portion of the genotypic variation in protein concentration and composition among wild soybeans. Strong positive correlation exists between the 11S:7S ratio and methionine or cysteine concentration of total protein. Moderate positive associations were found for threonine or tyrosine. A moderate negative correlation was found between lysine and 11S:7S. No association was found for leucine and phenylalanine or for total essential amino acid concentration. Based on these data, G. soja may contain a different complement of genes that influence expression of 11S and 7S proteins than G. max germplasm. Thus, through interspecific hybridization, wild soybeans may be a useful genetic resource for the further improvement of protein quality in cultivated soybeans.     

Further studies on artificial geometrical isomers of α-linolenic acid in edible linolenic acid-containing oils

Fifteen samples of commercial edible soybean and rapeseed oils (and mixtures of these) from Belgium, Great Britain and Germany have been analyzed for theirtrans-polyunsaturated fatty acid content. Only one sample out of the 13 refined samples, and the two cold-pressed samples, contained trace amounts oftrans isomers. Others contained between 1 and 3.3% of their total fatty acids as geometrical isomers of linoleic and linolenic acids. The degree of isomerization (DI) of linolenic acid varied between 10.5 and 26.9%. Combining results obtained in this study together with corresponding data for French oils (totalling 21 samples) indicates that the relative percentages of individual linolenic acid geometrical isomers depend on linolenic acid DI. Relationships linking these parameters could be approximated by straight lines, at least for DIs lying between 9 and 30%. Extrapolation to DI=0 suggests that the relative probabilities of isomerization of double bonds in positions 9, 12, and 15 are 41.7, 6.1 and 52.1%, respectively, at the very beginning of the isomerization reaction. At that time, the probability of a simultaneous isomerization of double bonds in positions 9 and 15 is close to zero. Thet,c,t isomer is apparently formedvia thec,c,t and thet,c,c isomers, the former being somewhat more prone to a second geometrical isomerization than the latter. The relative proportion of thec,t,c isomer is practically independent from the DI, at least between 9 and 30%, which would suggest that this isomer is an “end-product” of thecis-trans isomerization reaction.     

Molecular markers associated with linolenic acid content in soybean

An altered FA profile with decreased linolenic (18∶3) acid in soybean germplasm was developed by crossing N97-3708-13, a soybean line with reduced 18∶3 (<5.4%) and ‘Anand’, a normal soybean cultivar (9.7% 18∶3). The resulting recombinant inbred lines are promising because they may promote healthier oil with improved oxidative stability and flavor. The objective of this study was to utilize the population N97-3708-13 × Anand to identify simple sequence repeat (SSR) markers associated with 18∶3 content. Two markers, Satt534 and Satt560, which are located approximately 10 cM apart from each other, near the Fan locus on linkage group B2, were identified as quantitative trait loci significantly associated with 18∶3 content (P=0.001, R ²=0.59, individually). The SSR markers identified in this study should be useful for implementation of marker-assisted selection for low-18∶3 genotypes in soybean breeding programs.     

Production of linolenic acid in yeast cells expressing an omega-3 desaturase from tung (<Emphasis Type="Italic">Aleurites fordii</Emphasis>)

Tung oil is an industrial drying oil containing ca. 90% PUFA. We previously reported on enzymes required for the synthesis of linoleic (6% of FA) and eleostearic (80%) acids and here describe the cloning and functional analysis of an omega-3 FA desaturase (FAD3) required for the synthesis of linolenic acid (1%). The tung FAD3 cDNA was identified by screening a tung seed cDNA library using the polymerase chain reaction and degenerate primers encoding conserved regions of the FAD3 enzyme family. Expression of this cDNA in yeast cells, cultured in the presence of linoleic acid, resulted in the synthesis and accumulation of linolenic acid, which accounted for up to 18% w/w of total cellular FA. Tung FAD3 activity was significantly affected by cultivation temperature, with the greatest amount of linolenic acid accumulating in yeast cells grown at 15°C. The amount of linolenic acid synthesized in yeast cells by tung FAD3 is ca. 10-fold higher than that observed by expression of a rapeseed (Brassica napus) FAD3 in yeast, suggesting that tung FAD3 might be useful for biotechnological production of omega-3 FA in transgenic organisms.